This invention relates to a method for manufacturing an organic electro-luminescent display device, and more particularly to an organic electro-luminescent display device including an organic electro-luminescent medium and an electronic-device being manufactured after this method.
A conventional organic electro-luminescent element includes a transparent film-like ITO electrode formed on a glass substrate, a hole transport layer arranged on the ITO electrode though as to cover it, a film-like luminous layer formed on the hole transport layer, and an upper electrode formed on the luminous layer.
In the conventional electro-luminescent element thus constructed, when a negative DC voltage and a positive DC voltage are applied to the upper electrode and ITO electrode, respectively, holes injected from the ITO electrode are injected into the luminous layer while being transported through the hole transport layer. Whereas, electrons are injected from the upper electrode in the luminous layer, so that the electrons thus injected and the holes injected from the hole transport layer are recombined with each other in the luminous layer.
Such a recombination leads to luminescence of the luminous layer, which may be observed through the light-permeable hole transport layer, ITO electrode and glass substrate.
An organic electro-luminescent display device utilizing a luminous principle of the electro-luminescent element thus formed is constructed in such a manner that a plurality of ITO electrodes each acting as a lower electrode are formed in a stripe-like manner and a plurality of upper electrodes are arranged in a stripe-like manner and so as to extend in a direction perpendicular to the stripe-like ITO electrodes, resulting in forming a matrix by cooperation between the ITO electrodes and the upper electrodes. Then, the matrix is scanned by a drive means, so that luminescence of picture cells defined at intersections on the matrix is controlled in order by an image signal, leading to display of an image.
In such image display, resolution is determined depending on a width of each of the ITO electrodes and upper electrodes arranged in a stripe-like manner. The width is desirably as small as ten microns or less in view of resolution required.
In general, the ITO electrodes and upper electrodes each are formed by mask deposition. Unfortunately, the mask deposition fails to form a fine pattern as small as 0.1 mm or less. Wet chemical patterning technics permit formation of fine or precise patterns. However, wet etching causes an organic electro-luminescent medium to be contacted with an etching liquid or the like, to thereby be deteriorated in characteristics, so that the quality of image display and durability thereof is deteriorated.
An organic electro-luminescent display device and method for manufacturing the same which is intended to solve such a problem as described above is proposed in U.S. Pat. No. 5,804,917. This display device includes a lower substrate made of a transparent material, which has a plurality of light-permiable transparent electrodes made of ITO or the like and arranged thereon in a stripe-like manner. The display device further includes an organic layer made of an organic electro-luminescent medium and arranged between each adjacent two of a plurality of ribs so as to extend in a direction perpendicular to the transparent electrodes. The organic layers each have an upper elctrode formed on only a whole upper surface thereof. The upper electrodes are arranged in a stripe-like manner. The ribs are made of an insulating material and arranged so as to be spaced from each other at predetermined intervals and extend in a direction perpendicular to the transparent electrodes. The ribs each function as a spacer for supporting an upper substrate and lower transparent substrate while spacing both substrates from each other at a predetermined interval. The ribs may be made of a suitable material such as a lead glass having a black pigment added thereto or the like and arranged so as to be perpendicular to the transparent electrodes.
Between each adjacent two of the ribs the organic layer acting as a light emitter and the upper electrodes which are in the form of a thin film are laminatedly arranged in order. The organic layers and upper electrodes are arranged so as to be perpendicular to the transparent electrodes.
Manufacturing of the display device constructed in such a manner as described above and in particular forming of the upper electrodes requires quite complicated process steps. The upper electrodes are formed in the form of a film on the organic layer. In one suggested process the process is a mask-less process which takes place without using a mask. More particularly, a conductive material for the upper electrodes is deposited on the transparent electrodes on which the organic layers and ribs are formed. Then, a portion of the material formed on the ribs is removed by scraping, rubbing or the like. Removing of the conductive material formed on the ribs has to be carried out by using a mechanical process, thereby adding costs for manufacturing.